Luminescent lanthanide complexes with imine ligands and devices made with such complexes

ABSTRACT

The present invention is generally directed to luminescent lanthanide compounds with imine ligands, and devices that are made with the lanthanide compounds.

RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/195,942filed Jul. 15, 2002, now U.S. Pat. No. 6,924,047, which claims thebenefit of U.S. Provisional Application No. 60/306,395 filed Jul. 18,2001, the content of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to luminescent complexes of lanthanide metalswith imine ligands. It also relates to electronic devices in which theactive layer includes a lanthanide complex.

2. Description of the Related Art

Luminescent compounds are of interest in a variety of applications,including analytical, bio-analytical and electronic uses. Extensivestudies have been made of compounds of the lanthanide metals because oftheir characteristic sharp emission spectra with very narrowpeak-widths. Analytical uses of luminescent complexes of lanthanidemetals have been disclosed by, for example, Bell et al. in EP 556 005and EP 744 451. Electronic devices using luminescent organometalliccomplexes of lanthanide metals have also been disclosed. In most devicesthe lanthanide centers are bound to diimine ligands, such as Skotheim etal., U.S. Pat. No. 5,128,587, and Borner et al., U.S. Pat. No.5,756,224. Heeger et al. have reported devices using europium complexesblended with semiconducting conjugated polymers (Adv. Mater. 1999, 11,1349). Devices containing lanthanide centers bound to phosphineoxideligands have been disclosed in, for example, Kathirgamanathan et al. WO98/58037, Wenlian et al. Journal of the SID 1998, 6, 133, and Gao et al.Appl. Phys. Lett. 1998, 72, 2217.

There is a continuing need for improved luminescent lanthanidecompounds. Futhermore, the synthesis and luminescent properties oflanthanide imine compounds have remained largely unexplored.

SUMMARY OF THE INVENTION

The present invention is directed to a luminescent compound comprising alanthanide metal complexed to at least one imine ligand. It also isdirected to an organic electronic device having at least one emittinglayer comprising (a) at least one lanthanide compound having at leastone imine ligand, and, optionally, (b) a charge transport material. Asused herein, the term “imine ligand” is intended to mean a ligandderived from a compound having at least one imine group, —R—N═R—. Theimine is selected from a mono-imine having a Formula I, shown in FIG. 1,and a diimine having a Formula II, shown in FIG. 2, where:

-   -   in Formulae I and II:        -   R¹ can be the same or different at each occurrence and is            selected from alkyl, fluorinated alkyl, aryl, heteroalkyl,            heteroaryl, -QR², -QN(R²)₂, X, or adjacent R¹ groups can            join to form 5-membered or 6-membered rings,        -   R² is alkyl or aryl,        -   Q is a single bond, alkylene, arylene, or —C(O)—,        -   X is Cl, F, Br, or —CN,        -   alpha is an integer from 1 to 4;    -   in Formula II:        -   γ is an integer from 1 to 3, and        -   δ is 0 or an integer from 1 to 3,        -   with the provision that in Formula II there is at least one            R¹ group that is a fluorinated alkyl or X where X═F.

As used herein, the term “compound” is intended to mean an electricallyuncharged substance made up of molecules that further consist of atoms,wherein the atoms cannot be separated by physical means. The term“ligand” is intended to mean a molecule, ion, or atom that is attachedto the coordination sphere of a metallic ion. The term “complex”, whenused as a noun, is intended to mean a compound having at least onemetallic ion and at least one ligand. The term “group” is intended tomean a part of a compound, such as a substituent in an organic compoundor a ligand in a complex. The term “β-dicarbonyl” is intended to mean aneutral compound in which two ketone groups are present, separated by aCHR group. The term “β-enolate” is intended to mean the anionic form ofthe β-dicarbonyl in which the H from the CHR group between the twocarbonyl groups has been abstracted. The term “charge transportmaterial” is intended to mean material that can receive a charge from anelectrode and move it through the thickness of the material withrelatively high efficiency and low loss. The phrase “adjacent to,” whenused to refer to layers in a device, does not necessarily mean that onelayer is immediately next to another layer. On the other hand, thephrase “adjacent R groups” is used to refer to R groups that are next toeach other in a chemical formula (i.e., R groups that are on atomsjoined by a bond). The term “photoactive” refers to any material thatexhibits electroluminescence and/or photosensitivity. In addition, theIUPAC numbering system is used throughout, where the groups from thePeriodic Table are numbered from left to right as 1-18 (CRC Handbook ofChemistry and Physics, 81^(st) Edition, 2000).

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows Formula I for a mono-imine ligand useful in the invention.

FIG. 2 shows Formula II for a diimine ligand useful in the invention.

FIG. 3 shows Formula V for the β-enolate ligand useful in the invention.

FIG. 4 shows Formula VII for a phenylpyridine ligand.

FIG. 5 is a schematic diagram of a light-emitting device (LED).

FIG. 6 is a schematic diagram of an LED testing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the lanthanide compounds of the invention, the lanthanide metals arein the +3 oxidation state, and are heptacoordinate or octacoordinate.One or more of the coordination sites are occupied by at least oneligand having one of Formulae I and II. More than one of these ligands,and more than one type of ligand may be coordinated to the metal. Sixcoordination positions are occupied by β-enolate ligands, and one or twocoordination positions are occupied by the mono-imine or diimine ligand.The preferred lanthanide metals are Eu, Tb, and Tm. The preferredlanthanide complexes are neutral and non-ionic, and can be sublimedintact.

When the lanthanide compound is applied as a layer by vapor depositiontechniques, the ligands are generally chosen so that the final compoundis neutral in charge. It is preferred that the additional ligands areβ-enolates. More preferred lanthanide compounds are described by one ofFormulae III-A, III-B, or IV below:

Ln(β-enolate)₃(mono-imine)₁ (III-A) Ln(β-enolate)₃(mono-imine)₂ (III-B)Ln(β-enolate)₃(diimine) (IV)Where:

-   -   in Formulae (III-A) and (III-B):        -   mono-imine has Formula I of FIG. 1 as described above; and    -   in Formula (IV):        -   diimine has Formula II of FIG. 2 as described above.

Preferred mono-imine ligands include pyridine ligands (having Formula I)with at least one R¹ group including C_(n)(H+F)_(2n+1), where n is aninteger from 1 to 12; —CN; —(C₆H₅); —(C₄H₃S); and —(C₄H₃O).

Examples of suitable mono-imine ligands having Formula I, shown in FIG.1, include those listed in Table (i) below.

TABLE (i) 3-cyanopyridine [3-CNpy] 2-dimethylaminopyridine [2-dmapy]isoquinoline [isoq] 4-tertbutyl-pyridine [4-tbpy] 4-phenylpyridine[4-phpy] 2-(2-thienyl)pyridine [2-tpy] 4-cyanopyridine 4-CNpy

Preferred diimine ligands include bipyridine ligands (having Formula II)with at least one R¹ groups are —C_(n)(H+F)_(2n+1) and —C₆H_(m)F_(5−m),where m is an integer from 1 to 5.

Examples of suitable diimine ligands having Formula II shown in FIG. 2include those listed in Tabe (ii) below.

TABLE (ii) 5,5′-bis(trifluoromethyl)-2,2′-bipyridine [FMbipy]4,4′-bis(2-trifluoromethylphenyl)-2,2′-bipyridine [2-FMPbipy]4,4′-bis(3-trifluoromethylphenyl)-2,2′-bipyridine [3-FMPbipy]bis(4-fluorophenyl)-2,2′-bipyridine [FPbipy]

In some cases, the diimine and mono-imine ligands are commerciallyavailable from, for example, Aldrich Chemical Company (Milwaukee, Wis.).“FMbipy” can be prepared according to: Furue, Masaoki; Maruyama,Kazunori; Oguni, Tadayoshi; Naiki, Masahiro; Kamachi, Mikiharu InorgChem. 1992, 31(18), 3792-5. “2-FMPbipy”, “3-FMPbipy”, and “FPbipy” canbe prepared by Suzuki coupling, according to analogous literatureprocedures found in: Damrauer, Niels H.; Boussie, Thomas R.; Devenney,Martin; McCusker, James K. J. Am. Chem. Soc. 1997, 119(35), 8253-8268.

β-Enolate Ligands

The β-enolate ligands generally have Formula V shown in FIG. 3, where R³is the same or different at each occurrence. The R³ groups can behydrogen, halogen, substituted or unsubstituted alkyl, aryl, alkylarylor heterocyclic groups. Adjacent R³ groups can be joined to form five-and six-membered rings, which can be substituted. Preferred R³ groupsare selected from H, F, C_(n)(H+F)_(2n+1), —C₆H₅, —C₄H₃S, and —C₄H₃O,where n is an integer from 1 to 12, preferably from 1 to 6.

Examples of suitable β-enolate ligands include but are not limited tothe compounds listed in Table (iii) below. The abbreviation for theβ-enolate form is given in brackets.

TABLE (iii) 2,4-pentanedionate [acac] 1,3-diphenyl-1,3-propanedionate[DI] 2,2,6,6-tetramethyl-3,5-heptanedionate [TMH]4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate [TTFA]7,7-dimethyl-1,1,1,2,2,3,3-heptafluoro-4,6- [FOD] octanedionate1,1,1,5,5,5-hexafluoro-2,4-pentanedionate [F₆acac]1,1,1,3,5,5,5-heptafluoro-2,4-pentanedionate [F₇acac]1-phenyl-3-methyl-4-i-butyryl-5-pyrazolinonate PMBP

The β-dicarbonyls are generally available commercially.1,1,1,3,5,5,5-heptafluoro-2,4-pentanedionate, CF₃C(O)CFHC(O)CF₃, can beprepared using a two-step synthesis, based on the reaction ofperfluoropentene-2 with ammonia, followed by a hydrolysis step. Thiscompound should be stored and reacted under anyhydrous conditions as itis susceptible to hydrolysis.

The lanthanide complexes of the invention are made using two routes. Thefirst is by reacting the imine ligand with a Ln(b-enolate)₃ complex.Alternatively, these complexes can be obtained by the addition of theb-dicarbonyl and imine compounds to a simple lanthanide metal salt, suchas the chloride, nitrate, or acetate. For example, one synthetic methodis to dissolve an anhydrous lanthanide acetate, the desired b-dicarbonyland the imine in dichloromethane. The product can be precipitated by theaddition of hexanes. This is particularly useful for forming complexeswith heptafluoroacetylacetone. The heptafluoroacetylacetonato lanthanidecomplexes are generally quite stable to air and moisture.

Examples of lanthanide complexes having Formula III-A or Formula III-Babove with imines having Formula I, are given in Table 1 below:

TABLE 1 Compound Ln β-enolate mono-imine Formula 1-a Eu TTFA 4-CNpyIII-B 1-b Eu TTFA 2-dmapy III-A 1-c Eu TTFA isoq III-B 1-d Eu TTFA4-tbpy III-B 1-e Eu TTFA 4-phpy III-B 1-f Eu TTFA 2-tpy III-A 1-g TbAcac 4-CNpy III-B 1-h Tb Acac 2-dmapy III-A 1-i Tb Acac isoq III-B 1-jTb Acac 4-tbpy III-B 1-k Tb Acac 4-phpy III-B 1-l Tb Acac 2-tpy III-A

Examples of lanthanide complexes having Formula IV with diimines havingFormula II, are given in Table 2 below:

TABLE 2 Compound Ln β-enolate diimine 2-a Eu Acac FMbipy 2-b Eu Acac3-FMPbipy 2-c Eu Acac FPbipy 2-d Eu DI FMbipy 2-e Eu DI 3-FMPbipy 2-f EuDI FPbipy 2-g Eu TMH FMbipy 2-h Eu TMH 3-FMPbipy 2-i Eu TMH FPbipy 2-jEu TTFA FMbipy 2-k Eu TTFA 3-FMPbipy 2-l Eu TTFA FPbipy 2-m Tb acacFMbipy 2-n Tb acac 3-FMPbipy 2-o Tb acac FPbipy 2-p Tb DI FMbipy 2-q TbDI 3-FMPbipy 2-r Tb DI FPbipy 2-s Tb TMH FMbipy 2-t Tb TMH 3-FMPbipy 2-uTb TMH FPbipy 2-v Tm acac FMbipy 2-w Tm acac 3-FMPbipy 2-x Tm acacFPbipy 2-y Tm TMH FMbipy 2-z Tm TMH 3-FMPbipy 2-aa Tm TMH FPbipyElectronic Device

The present invention also relates to an electronic device comprising atleast one photoactive layer positioned between two electrical contactlayers, wherein the at least one photoactive layer of the deviceincludes the lanthanide complex of the invention. As shown in FIG. 4, atypical device 100 has an anode layer 110 and a cathode layer 150 andelectroactive layers 120, 130 and optionally 140 between the anode 110and cathode 150. Adjacent to the anode is a hole injection/transportlayer 120. Adjacent to the cathode is an optional layer 140 comprisingan electron transport material. Between the hole injection/transportlayer 120 and the cathode (or optional electron transport layer) is thephotoactive layer 130.

Depending upon the application of the device 100, the photoactive layer130 can be a light-emitting layer that is activated by an appliedvoltage (such as in a light-emitting diode or light-emittingelectrochemical cell), a layer of material that responds to radiantenergy and generates a signal with or without an applied bias voltage(such as in a photodetector). Examples of photodetectors includephotoconductive cells, photoresistors, photoswitches, phototransistors,and phototubes, and photovoltaic cells, as these terms are describe inMarkus, John, Electronics and Nucleonics Dictionary, 470 and 476(McGraw-Hill, Inc. 1966).

The lanthanide complexes of the invention are useful in the photoactivelayer 130 of the device. For some lanthanide complexes (such as Tb andEu), the luminescence spectrum is due to f-f transitions within themetal. Thus, while the intensity of emission can be influenced by thenature of the ligands attached to the lanthanide metal, the wavelengthremains relatively constant for all complexes of the same metal. Theeuropium complexes typically have a sharp red emission; the terbiumcomplexes have a sharp green emission. For some lanthanides (such asTm), the luminescence observed is not due to atomic transitions of themetal. Rather, it is due to either the ligands or the metal-ligandinteraction. Under such conditions, the luminescence band can be broadand the wavelength can be sensitive to the ligand used.

While the complexes can be used alone in the light-emitting layer, theiremission generally is not strong. It has been found that emission can begreatly improved by combining the lanthanide complexes with materialswhich facilitate charge transport. The materials can be hole transportmaterials, electron transport materials or other light-emittingmaterials which have good transport properties. If the lanthanidecomplex does not have good hole transport properties, a hole transportmaterial can be co-deposited. Conversely, an electron transport materialcan be co-deposited if the lanthanide complex does not have goodelectron transport properties. Some materials can transport bothelectrons and holes and are more flexible to use.

To achieve a high efficiency LED, the HOMO (highest occupied molecularorbital) of the hole transport material should align with the workfunction of the anode, the LUMO (lowest un-occupied molecular orbital)of the electron transport material should align with the work functionof the cathode. Chemical compatibility and sublimation temp of thematerials are also important considerations in selecting the electronand hole transport materials.

It is preferred to use hole transport materials such asN,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine(“TPD”) and bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (“MPMP”); electronand hole transporting material such as 4,4′-N,N′-dicarbazole biphenyl(“BCP”); or light-emitting materials with good electron and holetransport properties, such as chelated oxinoid compounds, such astris(8-hydroxyquinolato)aluminum (“Alq_(3”)), and cyclometalated iridiumcomplexes with 2-phenylpyridines and derivatives.

The iridium complexes have been described in copending application Ser.No. 60/215,362. They can be generally described as compound havingFormula VI below:IrL^(a)L^(b)L^(c) _(x)L′_(y)L″_(z),  (VI)

-   -   where:    -   x=0 or 1, y=0, 1 or 2, and z=0 or 1, with the proviso that:        -   x=0 or y+z=0 and        -   when y=2 then z=0;    -   L′=a bidentate ligand or a monodentate ligand, and is not a        phenylpyridine, phenylpyrimidine, or phenylquinoline; with the        proviso that:        -   when L′ is a monodentate ligand, y+z=2, and        -   when L′ is a bidentate ligand, z=0;    -   L″=a monodentate ligand, and is not a phenylpyridine, and        phenylpyrimidine, or phenylquinoline; and    -   L^(a), L^(b) and L^(c) are alike or different from each other        and each of L^(a), L^(b) and L^(c) has Formula VII, shown in        FIG. 4    -   wherein:    -   adjacent pairs of R⁴-R⁷ and R⁸-R¹¹ can be joined to form a five-        or six-membered ring,    -   at least one of R⁴-R¹¹ is selected from F, C_(s)F_(2s+1),        OC_(s)F_(2s+1), and OCF₂Y,    -   s is an integer from 1 to 6,    -   Y is H, Cl, or Br, and    -   A is C or N, provided that when A is N, there is no R⁴.

Preferred iridium compounds include those where L^(a), L^(b) and L^(c)are alike, and either (i) R⁶ is CF₃, R¹⁰ is F, and all other R are H; or(ii) R⁹ is CF₃ and all other R are H. The iridium complexes above aregenerally prepared from the appropriate substituted 2-phenylpyridine,phenylpyrimidine, or phenylquinoline. The substituted 2-phenylpyridines,phenylpyrimidines, and phenylquinolines are prepared, in good toexcellent yield, using the Suzuki coupling of the substituted2-chloropyridine, 2-chloropyrimidine or 2-chloroquinoline witharylboronic acid as described in O. Lohse, P. Thevenin, E. WaldvogelSynlett, 1999, 45-48. The iridium complex can then be prepared byreacting an excess of the 2-phenylpyridine, phenylpyrimidine, orphenylquinoline, without a solvent, with iridium trichloride hydrate and3 equivalents of silver trifluoracetate.

When the lanthanide complex is co-deposited with additional chargetransport material to form the photoactive layer, the lanthanide complexis generally present in an amount of about up to 85% by volume (15% byvolume for the charge transport material) based on the total volume ofthe emitting layer. Under such conditions the charge transport materialis responsible for carrying the electrons and/or holes to thelanthanide. The concentration of the charge transport material has to beabove the percolation threshold of approximately 15 volume %, such thata conducting pathway can be established. When the density of thematerial is close to one, 15 wt % is acceptable as long as thepercolation threshold is reached. The lanthanide complex is generallypresent in an amount of about 0.5 to 75% by weight, based on the totalweight of the emitting layer.

In some cases the lanthanide complexes may be present in more than oneisomeric form, or mixtures of different complexes may be present. Itwill be understood that in the above discussion of devices, the term“the lanthanide compound” is intended to encompass mixtures of compoundsand/or isomers.

The device generally also includes a support (not shown) which can beadjacent to the anode or the cathode. Most frequently, the support isadjacent the anode. The support can be flexible or rigid, organic orinorganic. Generally, glass or flexible organic films are used as asupport. The anode 110 is an electrode that is particularly efficientfor injecting or collecting positive charge carriers. The anode ispreferably made of materials containing a metal, mixed metal, alloy,metal oxide or mixed-metal oxide. Suitable metals include the Group 11metals, the metals in Groups 4, 5, and 6, and the Group 8-10 transitionmetals. If the anode is to be light-transmitting, mixed-metal oxides ofGroups 12, 13 and 14 metals, such as indium-tin-oxide, are generallyused. The anode 110 may also comprise an organic material such aspolyaniline as described in “Flexible light-emitting diodes made fromsoluble conducting polymers,” Nature vol. 357, pp 477-479 (11 Jun.1992).

The anode layer 110 is usually applied by a physical vapor depositionprocess or spin-cast process. The term “physical vapor deposition”refers to various deposition approaches carried out in vacuo. Thus, forexample, physical vapor deposition includes all forms of sputtering,including ion beam sputtering, as well as all forms of vapor depositionsuch as e-beam evaporation and resistance evaporation. A specific formof physical vapor deposition which is useful is rf magnetron sputtering.

There is generally a hole transport layer 120 adjacent the anode.Examples of hole transport materials for layer 120 have been summarizedfor example, in Kirk-Othmer Encyclopedia of Chemical Technology, FourthEdition, Vol. 18, p. 837-860, 1996, by Y. Wang. Both hole transportingmolecules and polymers can be used. Commonly used hole transportingmolecules, in addition to TPD and MPMP mentioned above, are:1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC),N,N′-bis(4-methylphenyl)-N,N′-bis(4-ethylphenyl)-[1,1′-(3,3′-dimethyl)biphenyl]-4,4′-diamine(ETPD), tetrakis-(3-methylphenyl)-N,N,N,′N′-2,5-phenylenediamine (PDA),a-phenyl-4-N,N-diphenylaminostyrene (TPS), p-(diethylamino)benzaldehydediphenylhydrazone (DEH), triphenylamine (TPA),1-phenyl-3-[p-(diethylamino)styryl]-5-[p-(diethylamino)phenyl]pyrazoline(PPR or DEASP), 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane (DCZB),N,N,N′,N′-tetrakis(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TTB),and porphyrinic compounds, such as copper phthalocyanine. Commonly usedhole transporting polymers are polyvinylcarbazole,(phenylmethyl)polysilane, poly(3,4-ethylendioxythiophene) (PEDOT), andpolyaniline. It is also possible to obtain hole transporting polymers bydoping hole transporting molecules such as those mentioned above intopolymers such as polystyrene and polycarbonate.

Optional layer 140 can function both to facilitate electron transport,and also serve as a buffer layer or anti-quenching layer to preventquenching reactions at layer interfaces. Preferably, this layer promoteselectron mobility and reduces quenching reactions. Examples of electrontransport materials for optional layer 140 include metal chelatedoxinoid compounds, such as tris(8-hydroxyquinolato)aluminum (Alq₃);phenanthroline-based compounds, such as2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (DDPA) or4,7-diphenyl-1,10-phenanthroline (DPA), and azole compounds such as2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) and3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole (TAZ).

The cathode 150 is an electrode that is particularly efficient forinjecting or collecting electrons or negative charge carriers. Thecathode can be any metal or nonmetal having a lower work function thanthe first electrical contact layer (in this case, an anode). Materialsfor the second electrical contact layer can be selected from alkalimetals of Group 1 (e.g., Li, Cs), the Group 2 (alkaline earth) metals,the Group 12 metals, the lanthanides, and the actinides. Materials suchas aluminum, indium, calcium, barium, samarium and magnesium, as well ascombinations, can be used.

It is known to have other layers in organic electronic devices. Forexample, there can be a layer (not shown) between the conductive polymerlayer 120 and the active layer 130 to facilitate positive chargetransport and/or band-gap matching of the layers, or to function as aprotective layer. Similarly, there can be additional layers (not shown)between the active layer 130 and the cathode layer 150 to facilitatenegative charge transport and/or band-gap matching between the layers,or to function as a protective layer. Layers that are known in the artcan be used. In addition, any of the above-described layers can be madeof two or more layers. Alternatively, some or all of inorganic anodelayer 110, the conductive polymer layer 120, the active layer 130, andcathode layer 150, may be surface treated to increase charge carriertransport efficiency. The choice of materials for each of the componentlayers is preferably determined by balancing the goals of providing adevice with high device efficiency.

It is understood that each functional layer may be made up of more thanone layer.

The device can be prepared by sequentially vapor depositing theindividual layers on a suitable substrate. Substrates such as glass andpolymeric films can be used. Conventional vapor deposition techniquescan be used, such as thermal evaporation, chemical vapor deposition, andthe like. Alternatively, the organic layers can be coated from solutionsor dispersions in suitable solvents, using any conventional coatingtechnique. In general, the different layers will have the followingrange of thicknesses: anode 110, 500-5000 Å, preferably 1000-2000 Å;hole transport layer 120, 50-2500 Å, preferably 200-2000 Å;light-emitting layer 130, 10-1000 Å, preferably 100-800 Å; optionalelectron transport layer 140, 50-1000 Å, preferably 100-800 Å; cathode150, 200-10,000 Å, preferably 300-5000 Å. The location of theelectron-hole recombination zone in the device, and thus the emissionspectrum of the device, is affected by the relative thickness of eachlayer. For example, when an emitter, such as Alq₃ is used as theelectron transport layer, the electron-hole recombination zone can be inthe Alq₃ layer. The emission would then be that of Alq₃, and not thedesired sharp lanthanide emission. Thus the thickness of theelectron-transport layer must be chosen so that the electron-holerecombination zone is in the light-emitting layer. The desired ratio oflayer thicknesses will depend on the exact nature of the materials used.

It is understood that the efficiency of the devices of the inventionmade with lanthanide compounds, can be further improved by optimizingthe other layers in the device. For example, more efficient cathodessuch as Ca, Ba or LiF can be used. Shaped substrates and novel holetransport materials that result in a reduction in operating voltage orincrease quantum efficiency are also applicable. Additional layers canalso be added to tailor the energy levels of the various layers andfacilitate electroluminescence.

EXAMPLES

The following examples illustrate certain features and advantages of thepresent invention. They are intended to be illustrative of theinvention, but not limiting. All percentages are by weight, unlessotherwise indicated. Complexes of the type Complexes (acac)₃Tb(phen),(TTFA)₃Eu(phen) and (TTFA)₃Eu(DPphen) were synthesized followingprocedures known in the art, such as Topilova, Z. M.; Gerasimenko, G.I.; Kudryavtseva, L. S.; Lozinskii, M. O.; Meshkova, S. B. Russian J.Inorg. Chem. 1989, 34, 1265.

EXAMPLE 1

Complexes 1-a through 1-l, having the Formulae III-A and III-B wereprepared by reacting the corresponding Ln(β-enolate)₃ with the desiredmono-imine in dichloromethane. The products were isolated by filtration.

EXAMPLE 2

Eu(TMH)₃(3-FMPbipy). To a MeOH/CH₂Cl₂ (3 mL, 1:2 ratio of the twosolvents) solution of 3-FMPbipy (0.148 g, 0.33 mmol) was added Eu(TMH)₃(0.234 g, 0.33 mmol) dissolved in MeOH (2 mL). The resulting solutionwas stirred at room temperature for 48 hours. After the solvent wasevaporated the white solid was washed with hexane to yield the product14% yield (0.050 g). ¹⁹F{¹H} NMR (CD₂Cl₂, 376 MHz) δ is −63.36.

EXAMPLE 3

Eu(TMH)₃(Fpbipy). To a MeOH/CH₂Cl₂ (3 mL, 1:2 ratio of the two solvents)solution of Fpbipy (0.187 g, 0.27 mmol) was added Eu(TMH)₃ (0.187 g,0.27 mmol) dissolved in MeOH (2 mL). The resulting solution was stirredat room temperature for 48 hours. After the solvent was evaporated thewhite solid was washed with hexane to yield the product 70% yield (0.138g).

Other complexes in Table 2 above were prepared in an analogous manner.

EXAMPLE 4

This example illustrates the formation of OLEDs using the lanthanidecomplexes of the invention.

Thin film OLED devices including a hole transport layer (HT layer),electroluminescent layer (EL layer) and an electron transport layer (ETlayer) were fabricated by the thermal evaporation technique. An EdwardAuto 306 evaporator with oil diffusion pump was used. The base vacuumfor all of the thin film deposition was in the range of 10⁻⁶ torr. Thedeposition chamber was capable of depositing five different filmswithout the need to break up the vacuum.

An indium tin oxide (ITO) coated glass substrate was used, having an ITOlayer of about 1000-2000 Å. The substrate was first patterned by etchingaway the unwanted ITO area with 1N HCl solution, to form a firstelectrode pattern. Polyimide tape was used as the mask. The patternedITO substrate was then cleaned ultrasonically in aqueous detergentsolution. The substrate was then rinsed with distilled water, followedby isopropanol, and then degreased in toluene vapor for about 3 hours.

The cleaned, patterned ITO substrate was then loaded into the vacuumchamber and the chamber was pumped down to 10⁻⁶ torr. The substrate wasthen further cleaned using an oxygen plasma for about 5-10 minutes.After cleaning, multiple layers of thin films for the HT, EL and ETlayers were then deposited sequentially onto the substrate by thermalevaporation. Finally, patterned metal electrodes of Al were depositedthrough a mask, with a thickness in the range of 700-760 Å. Thethicknesses of the films were measured during deposition using a quartzcrystal monitor (Sycon STC-200). The reported film thicknesses arenominal, calculated assuming the density of the material deposited to beone. The completed OLED device was then taken out of the vacuum chamberand characterized immediately without encapsulation. A summary of thedevice layers and thicknesses is given in Table 3, below.

The OLED samples were characterized by measuring the (1) current-voltage(I-V) curves, (2) electroluminescence radiance versus voltage, and (3)electroluminescence spectrum versus voltage. The apparatus used, 200, isshown in FIG. 6. The I-V curves of an OLED sample, 220, were measuredwith a Keithley Source-Measurement Unit Model 237, 280. Theelectroluminescence radiance (in the unit of cd/m²) vs. voltage wasmeasured with a Minolta LS-110 luminescence meter, 210, while thevoltage was scanned using the Keithley SMU. The electroluminescencespectrum were obtained by collecting light using a pair of lenses, 230,through an electronic shutter, 240, dispersed through a spectrograph,250, and then measured with a diode array detector, 260. All threemeasurements were performed at the same time and controlled by acomputer, 270. The efficiency of the device at certain voltage wasdetermined by dividing the electroluminescence radiance of the LED bythe current density needed to run the device. The unit of measurement isCd/A. The results are given in Table 3 below.

TABLE 3 Peak Peak Approximate Peak HT layer EL layer ET layer Radiance,efficiency, Wavelengths, Sample Thickness, Å thickness, Å thickness, Åcd/m² cd/A nm 1 MPMP Example 2, DDPA, 8 0.25 617 508 425 420 2 MPMPExample 3, DDPA, 2.5 0.16 617 535 441 403 DDPA =2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline ET = electron transport HT= hole transport MPMP =bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane

1. A lanthanide compound having Formula III-B below:Ln(β-enolate)₃(mono-imine)₂  (III-B) wherein the mono-imine is selectedfrom 3-cyanopyridine; 2-dimethylaminopyridine; isoquinoline;4-tertbutyl-pyridine; 4-phenylpyridine; and 2-(2-thienyl)pyridine. 2.The compound of claim 1 wherein Ln is selected from Eu, Tb and Tm. 3.The compound of claim 1 wherein the β-enolate is selected from2,4-pentanedionate; 1,3-diphenyl- 1,3-propanedionate;2,2,6,6-tetramethyl-3 ,5-heptanedionate;4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate;7,7-dimethyl-1,1,1,2,2,3,3-heptafluoro-4,6-octanedionate;1,1,1,5,5,5-hexaflouro-2,4-pentanedionate;1-phenyl-3-methyl-4-i-butyryl-pyrazolinonate; and1,1,1,3,5,5,5-heptafluoro-2,4-pentanedionate.
 4. An electronic devicecomprising a photoactive layer, wherein the photoactive layer comprisesthe lanthanide compound of claim
 1. 5. The device of claim 4 wherein thelanthanide compound is present in an amount of up to about 85% by volumebased on the total volume of the photoactive layer.
 6. The device ofclaim 4 wherein the photoactive layer further comprises (b) a chargetransport material.
 7. The device of claim 6 wherein the chargetransport material (b) is a hole transport material selected fromN,N′-diphenyl-N,N′-bis(3 -methylphenyl)-[1,1′-biphenyl]-4,4′-diamine andbis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane.
 8. Thedevice of claim 6 wherein the charge transport material (b) is anelectron and hole transporting material selected from4,4′-N,N′-dicarbazole biphenyl; chelated oxinoid compounds of aluminum;and cyclometalated iridium complexes with 2-phenylpyridines.
 9. Thedevice of claim 4, further comprising a hole transport layer, whereinthe hole transport layer comprises a hole transport material selectedfrom N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine; 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane;N,N′-bis(4-methylphenyl)-N,N′-bis(4-ethylphenyl)-[1,1′-(3,3′-dimethyl)biphenyl]-4,4′-diamine;tetrakis-(3-methylphenyl)-N,N,N′,N′-2,5-phenylenediamine;α-phenyl-4-N,N-diphenylaminostyrene; p-(diethylamino)benzaldehydediphenylhydrazone; triphenylamine;bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane;1-phenyl-3-[p-(diethylamino)styryl]-5-[p-(diethylamino)phenyl]pyrazoline; 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane;N,N,N′,N′-tetrakis(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine;porphyrinic compounds; and combinations thereof.
 10. The device of claim4, further comprising an electron transport layer, wherein the electrontransport layer comprises an electron transport material selected fromtris(8-hydroxyquinolato)aluminum; 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline; 4,7-diphenyl- 1,10-phenanthroline;2-(4-biphenylyl)-5 -(4-t-butylphenyl)- 1,3,4-oxadiazole;3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole; andcombinations thereof.
 11. A lanthanide compound having Formula III-BLn(β-enolate)₃(mono-imine)₂  (III-B) and having a structure selectedfrom compounds as provided in the below table, TABLE 1 Compound Lnβ-enolate mono-imine Formula 1-a Eu TTFA 4-CNpy III-B 1-c Eu TTFA isoqIII-B 1-d Eu TTFA 4-tbpy III-B 1-e Eu TTFA 4-phpy III-B 1-g Tb Acac4-CNpy III-B 1-i Tb Acac isoq III-B 1-j Tb Acac 4-tbpy III-B 1-k Tb Acac4-phpy III-B

wherein TTFA is 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate; Acac is2,4-pentanedionate; 4-CNpy is 4-cyanopyridine; isoq is isoquinoline;4-tbpy is 4-tertbutyl-pyridine; and 4-phpy is 4-phenylpyridine.